The present invention relates to a surface protection film for a liquid crystal display to be used for personal computers, word processors, TV and the like, a liquid crystal display protected with the surface protection film and a method for protecting the surface of a liquid crystal display with the surface protection film.
Liquid crystal displays are produced by laminating various optical elements such as a glass substrate, a liquid crystal, a polarizing plate (film), a phase plate (film), an anti-reflection film and the like, fixing the outer periphery with a fixing frame made of a metal plate of stainless and the like, which is called xe2x80x9cbezelxe2x80x9d, to give a liquid crystal module, assembling this liquid crystal module in a case together with other constituent members and housing the resulting structure. The display part of a liquid crystal display is generally covered with a surface protection film (sheet) in order to prevent adhesion of and contamination with dust and the like during the assembly step and distribution process of the products (merchandise). This is performed by applying the sheet onto the display surface of a liquid crystal module during the production of the module. Since the display part of a liquid crystal display, which is a final product, consists of a display part of a liquid crystal module, the surface of the display part of the module is covered with a surface protection film (sheet) during the production of the module.
The display surface is covered by adhering a surface protection adhesive sheet (laminate film) having a releasable adhesive layer formed on the entire area of one side surface of a film, such as a polyethylene film, a polypropylene film, a vinyl chloride film, a polyethylene terephthalate film and the like, to the display surface of a liquid crystal module, or by superimposing the above-mentioned polyethylene film, polypropylene film, vinyl chloride film, polyethylene terephthalate film and the like on the display surface of a liquid crystal module and fixing the outer periphery of the film with an adhesive tape, or by other method.
When the display surface of a liquid crystal module is covered with a protection film during the assembly of a liquid crystal display, however, changes in optical hue (color shading) are sometimes observed on the display surface when the protection film is peeled off, after distribution process, for actual use of the liquid crystal display, which degrades the reliability as a display unit.
In view of the above situation, the present invention aims at providing a surface protection film for a liquid crystal display, which is capable of suppressing changes in the optical hue (color shading) on the display surface of a liquid crystal display (display surface of a liquid crystal module), a liquid crystal display protected with the surface protection film, and a method for protecting the surface of a liquid crystal display with the surface protection film.
According to the present invention, the mechanism of changes in the optical hue (color shading), that are caused by the covering of the display surface of a liquid crystal module with a protection film, has been investigated and the following (i) to (iii) have been found.
(i) The changes in the optical hue (color shading) occur due to difference in the color between an area of the surface of a polarizing plate constituting the display surface of a liquid crystal module, where the protection film is not adhered closely (e.g., vicinity of bezel having uneven surfaces), and an area where the film is adhered closely, the former looking reddish.
(ii) The polarizing plate looks reddish because the polarizing plate absorbs moisture, which varies light transmittance.
(iii) The reddish color is produced by the greater absorption of moisture than in the area where the protection film is adhered closely.
The present invention is based on the finding that the use of a film, which shows moisture permeation above a certain amount under a specific environment, as a surface protection film can obliterate the occurrence of color shading on the display surface of a liquid crystal display. The present invention is characterized by the following features.
(1) A film for protecting a display surface of a liquid crystal display, which comprises a polymer film having a coefficient of bending stress k as expressed by the formula: k=Eh3, wherein E is a tensile elastic modulus (N/mm2) in the MD (machine direction) and h is a thicknessxc2x7(mm), of not less than 0.01 (Nxc2x7mm), and which shows an amount of moisture permeation at 35xc2x0 C., 80% RH (relative humidity) for 72 hours of not less than 100 g/m2xc2x772 hr.
(2) A film for protecting a display surface of a liquid crystal display, which comprises a laminate film comprising a polymer film having a coefficient of bending stress k as expressed by the formula: k=Eh3, wherein E is a tensile elastic modulus (N/mm2) in the MD (machine direction) and h is a thickness (mm), of not less than 0.01 (N mm), and an adhesive layer formed on one side of the polymer film, or a laminate film comprising the above polymer film, an adhesive layer formed on one side of the polymer film, and a back coating layer formed on the other side of the polymer film, and which has an amount of moisture permeation at 35xc2x0 C., 80% RH for 72 hours of not less than 100 g/m2xc2x772 hr.
(3) The protection film of (1) above, wherein the polymer film has been subjected to an antistatic treatment comprising adding an antistatic agent.
(4) The protection film of (2) above, wherein the laminate film has been subjected to an antistatic treatment comprising adding an antistatic agent to the adhesive layer and/or the polymer film, or forming an antistatic layer under the adhesive layer and/or the back coating layer.
(5) The protection film of (1) or (2) above, wherein the polymer film is selected from the group consisting of a cellulose film, a poly(vinyl alcohol) film, a nylon film, a polystyrene film and a poly(meth)acrylonitrile film.
(6) The protection film of (1) or (2) above, wherein the polymer film has a thickness of not less than 15 xcexcm.
(7) The protection film of (1) or (2) above, which makes a difference (xcex94a*) in a perception chromaticity index a*, as measured by a CIE1976 L*a*b* colorimetric system, between a partial display surface covered with the film and the display surface without the film, not more than 0.2, wherein the difference is obtained by covering a part of the display surface of a polarizing plate with the protection film, standing the polarizing plate at 35xc2x0 C., 80% RH for 72 hours, and determining the indices of the covered part and the uncovered part.
(8) A liquid crystal display comprising a display surface protected with the protection film of (1) or (2) above.
(9) A method for protecting a surface of a liquid crystal display, which comprises covering the display surface with the protection film of (1) or (2) above.
(10) A film for protecting a display surface of a liquid crystal display, which comprises a polymer film having a coefficient of bending stress k as expressed by the formula: k=Eh3, wherein E is a tensile elastic modulus (N/mm2) in the MD (machine direction) and h is a thickness (mm), of not less than 0.01 (Nxc2x7mm), and which shows an amount of moisture permeation at 35xc2x0 C., 80% RH for 72 hours of not less than 100 g/m2xc2x772 hr and not more than 7000 g/m2xc2x772 hr.
(11) A film for protecting a display surface of a liquid crystal display, which comprises a laminate film comprising a polymer film having a coefficient of bending stress k as expressed by the formula: k=Eh3, wherein E is a tensile elastic modulus (N/mm2) in the MD (machine direction) and h is a thickness (mm), of not less than 0.01 (Nxc2x7mm), and an adhesive layer formed on one side of the polymer film, or a laminate film comprising the above polymer film, an adhesive layer formed on one side of the polymer film, and a back coating layer formed on the other side of the polymer film, and which shows an amount of moisture permeation at 35xc2x0 C., 80% RH for 72 hours of not less than 100 g/m2xc2x772 hr and not more than 7000 g/m2xc2x772 hr.